/*
struct ListNode {
    int val;
    struct ListNode *next;
};
*/
//https://www.nowcoder.com/practice/b58434e200a648c589ca2063f1faf58c?tpId=295&tqId=654&ru=/exam/oj&qru=/ta/format-top101/question-ranking&sourceUrl=%2Fexam%2Foj%3Fpage%3D1%26tab%3D%25E7%25AE%2597%25E6%25B3%2595%25E7%25AF%2587%26topicId%3D295


class Solution {
public:
    ListNode* reverseBetween(ListNode* head, int m, int n){
        //加个表头
        ListNode* res = new ListNode(-1);
        res->next = head;
        //前序节点
        ListNode* pre = res;
        //当前节点
        ListNode* cur = head;
        //找到m
        for(int i = 1; i < m; i++){
            pre = cur;
            cur = cur->next;
        }
        //从m反转到n
        for(int i = m; i < n; i++){
            ListNode* temp = cur->next;
            cur->next = temp->next;
            temp->next = pre->next;
            pre->next = temp;           
        }
        //返回去掉表头
        return res->next;
    }
};